The present invention relates to a composition for forming molded and/or cast articles for machine parts, instruments, machine tools and the like; the method for forming such articles, and the molded and/or cast articles themselves.
Machine parts, machine tools and the like have been formed from compositions of sand, gravel, stone, natural or synthetic rock, held together by a binder. The articles made from such compositions are mostly thick-walled products, such as machine stands, or supports, where high rigidity, excellent inherent stability and good vibration and noise dampening properties are required. Due to the use of relatively cheap stone and rock as filler material, in high proportion to the binder, the machine parts and other articles made therefrom can be produced at low cost and in particular, with low energy expenditure, for example, at about 1/3 that of comparable parts made from aluminum and about 1/2 that of those made from steel.
However, the known compositions have several drawbacks, amongst which is the fact that strength, particularly the tensile strength and the bending strength, determined by the filler and the binder, is limited. The known compositions employing stone as a filler for conventional binders, have a maximum tensile strength of only 3-5 kg/mm.sup.2. Further, the flow and mold filling behavior of such compositions is determined to a great extent by the percentage of the rock dines in the filler. A high fine proportion of filler reduces the inherent stability of the finished workpiece. A low fine portion of the filler yields great inherent stability, although it renders the casting more difficult and results in large, porous areas inside the workpiece, as well as on the surface. Further, it is difficult to work or machine such compositions to critical dimensions.
It has been known to form compositions having a large proportion of glass fibers and plastic binder. Such compositions, however, are, by multiples, more expensive than the compositions utilizing stone and rock, and have far lower E-modulus. In addition, the coefficient of thermal expansion of such a composition is much more difficult to control and under certain circumstances, not possible to control at all.
It is the object of the present invention to overcome the disadvantages and difficulties of the known prior art, and to provide workpieces of inherent stability and strength, utilizing the relatively inexpensive stone and rock filler material.
It is a further object of the present invention to provide such compositions in which the stone and rock are employed as filler materials, which have a flow characteristic which enables them to be easily cast and molded and which permits the production of complicated molded parts with satisfactory surface smoothness and without undesired porosity or cavities therein.
The foregoing objects, as well as others, are set forth in the following disclosure of the present invention.